1. Field of the Invention
This invention lies in the field of control means for fuel oil supplied to burners. More particularly, it is the field of control means for control of the viscosity of fuel oil supplied to burners. Still more particularly, it is a control means for controlling the viscosity of fuel oil based upon a measurement of viscosity of the fuel oil by determining the variations in pressure drop through a constant dimension orifice, due to viscosity variations, and controlling the supply of steam to a fuel heater so as to alter the temperature and thus the viscosity, so as to maintain the viscosity at a selected value.
2. Description of the Prior Art
A serious problem associated with the burning of fuel oils is the control and maintenance of viscosity of the fuel oil as it is burned, to an optimum viscosity which is most desirable for the operation of the fuel burners. The reason is that for satisfactory and efficient burning of fuel oil, there is an optimum or preferred condition of minimal viscosity for the fuel oil as it is delivered for immediate burning, but the required temperature for suitable viscosity on different fuel oils may vary widely. Thus, a temperature of preheat which is satisfactory for one fuel oil, to reduce its viscosity as burned to an optimum condition, is not at all satisfactory for another fuel oil.
This problem has caused a number of entries into the art of viscosity control. One such entry relied on a vibrating reed for viscosity sensing and control. Another entry views the characteristic of constant oil flow across a viscosimeter orifice (reference page 22-39, Perry's Chemical Engineers Handbook, 4th Edition, McGraw-Hill).
A characteristic of the flow of viscous fluids, is that, as viscosity increases, there is interference with flow. For flow of a fixed quantity of viscous fluid the pressure drop increases as viscosity of the fluid increases, and vice versa. For a flow of viscous fluid at fixed pressure drop the quantity of fluid decreases as the viscosity increases and vice versa. In a fixed passageway, velocity of flow is directly proportional to quantity of flow, therefore, in this invention the control means is provided by a velocity variation.